The defence secretary has paved the way for air strikes on Islamic State targets in Syria, saying the extremists needed to be targeted "at source".
But Michael Fallon said no action would be taken without a Commons vote and a "consensus" among MPs.
The UK does not need the backing of MPs to launch raids but Mr Fallon has said they will have the final say.
Labour has indicated it would not oppose military action in Syria as it did in 2013.
The party's acting leader Harriet Harman said Islamic State had to be "stopped" and Labour would look "very seriously" at any proposals brought forward by the government.
She said the situation was the different from that in 2013, when Labour voted against air strikes in Syria, because IS was a terrorist organisation, while President Assad was the head of a government, albeit a "terrible regime".
Labour had been concerned about "what would fill the space" if the Syrian president had been toppled, added Ms Harman.
BBC diplomatic correspondent Jonathan Marcus examines what difference Syria IS air strikes could make
She suggested terrorist attacks, such as Friday's tourist murders in Tunisia, may have been planned by IS in Syria - a point also made by Michael Fallon.
Thirty of the 38 tourists killed on the beach in Sousse on 26 June have been confirmed as British. Student Seifeddine Rezgui, 23, said to have had links to IS, was shot dead by police after carrying out the attack.
Mr Fallon told MPs a "full spectrum response" was needed to deal with IS at its source.
"We will not bring a motion to this house on which there is not some consensus.

"Our position therefore remains that we would return to this house before conducting air strikes in Syria."
BBC political editor Nick Robinson said Mr Fallon's comments were not a call for imminent action, but were "preparing the ground" or "pitch rolling" for a change in approach.
Prime Minister David Cameron later said IS posed "an existential threat" to the West, and its members in Iraq and Syria were plotting "terrible attacks" on British soil.
Downing Street said Mr Cameron believed MPs should be thinking about whether UK forces should be doing more to tackle IS.
But Mr Cameron's official spokeswoman said the issue of further military action needed to be considered "properly and carefully" before any decision was taken to ask MPs to back any specific action.
She said Britain was already flying surveillance and air-to-air re-fuelling operations over Syria.
'Pitch rolling'
Mr Cameron was defeated in the Commons in 2013 when Tory rebels joined forces with Labour to oppose air strikes on Syrian government targets designed to deter the use of chemical weapons.
The 2013 vote focused on the Syrian President Bashar al-Assad, not IS militants.
Parliament approved UK bombing of militant positions in Iraq last year. However, MPs were not asked at the time to authorise strikes across the border in Syria.

Remember when Cameron puffed out his chest and said IS will be smashed, yea hows that working out for you David.

Engaging them in Syria would have an effect, but only if it wasn't limited to air strikes. It's a shame that none of the Western countries with reason to act would ever consider a full-scale occupation.

Engaging them in Syria would have an effect, but only if it wasn't limited to air strikes. It's a shame that none of the Western countries with reason to act would ever consider a full-scale occupation.

Yeah, because it worked so well in Iraq and Afghanistan. Trillions of dollars and thousands of lives for people that don't even know what help looks like.

They were unaware that they had killed the strategic head of the group calling itself "Islamic State" (IS). The fact that this could have happened at all was the result of a rare but fatal miscalculation by the brilliant planner. The local rebels placed the body into a refrigerator, in which they intended to bury him. Only later, when they realized how important the man was, did they lift his body out again.

Samir Abd Muhammad al-Khlifawi was the real name of the Iraqi, whose bony features were softened by a white beard. But no one knew him by that name. Even his best-known pseudonym, Haji Bakr, wasn't widely known. But that was precisely part of the plan. The former colonel in the intelligence service of Saddam Hussein's air defense force had been secretly pulling the strings at IS for years. Former members of the group had repeatedly mentioned him as one of its leading figures. Still, it was never clear what exactly his role was.

But when the architect of the Islamic State died, he left something behind that he had intended to keep strictly confidential: the blueprint for this state. It is a folder full of handwritten organizational charts, lists and schedules, which describe how a country can be gradually subjugated. SPIEGEL has gained exclusive access to the 31 pages, some consisting of several pages pasted together. They reveal a multilayered composition and directives for action, some already tested and others newly devised for the anarchical situation in Syria's rebel-held territories. In a sense, the documents are the source code of the most successful terrorist army in recent history.
(....)The Master Plan

The story of this collection of documents begins at a time when few had yet heard of the "Islamic State." When Iraqi national Haji Bakr traveled to Syria as part of a tiny advance party in late 2012, he had a seemingly absurd plan: IS would capture as much territory as possible in Syria. Then, using Syria as a beachhead, it would invade Iraq.
(....)

The Beginnings in Iraq

It seemed as if George Orwell had been the model for this spawn of paranoid surveillance. But it was much simpler than that. Bakr was merely modifying what he had learned in the past: Saddam Hussein's omnipresent security apparatus, in which no one, not even generals in the intelligence service, could be certain they weren't being spied on.
(....)

There is a simple reason why there is no mention in Bakr's writings of prophecies relating to the establishment of an Islamic State allegedly ordained by God: He believed that fanatical religious convictions alone were not enough to achieve victory. But he did believe that the faith of others could be exploited.
(....)

...You should read the article for all the details i left out, and this was not even 1/10th of the article

(...)
It's what ISIS has been wanting all along, a great big Sunni/Shia fight to the death...... Iran and Sadr will give it to them..... Maybe the Saudis will jump in, it will be great.

And we can sit back and let them do their thing, and see where it stands when the dust settles.
(...)

ISIS kills both sunni's & shia..
They brainwashed their fighters so they wont know who's who but are loyal to the isis comanders no mather what..

Anyway, ISIS desperately wants total war between shia/sunni . And that it spills to the neighbouring country's as well.
So they can use the gaos to create a ("islamic") super power in all of this territory..
Bit spooky but they might be able to bring peace to the entire place.. but more like a dictatorship kinda peace lol